netdev - [PATCH net-next v2 0/2] Make TIME-WAIT reuse delay deterministic and configurable

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Message-Id: <20241209-jakub-krn-909-poc-msec-tw-tstamp-v2-0-66aca0eed03e@cloudflare.com>
Date: Mon, 09 Dec 2024 20:38:02 +0100
From: Jakub Sitnicki <jakub@...udflare.com>
To: netdev@...r.kernel.org, "David S. Miller" <davem@...emloft.net>, 
 Eric Dumazet <edumazet@...gle.com>, Jakub Kicinski <kuba@...nel.org>, 
 Paolo Abeni <pabeni@...hat.com>
Cc: Jason Xing <kerneljasonxing@...il.com>, 
 Adrien Vasseur <avasseur@...udflare.com>, 
 Lee Valentine <lvalentine@...udflare.com>, kernel-team@...udflare.com
Subject: [PATCH net-next v2 0/2] Make TIME-WAIT reuse delay deterministic
 and configurable

This patch set is an effort to enable faster reuse of TIME-WAIT sockets.
We have recently talked about the motivation and the idea at Plumbers [1].

Experiment in production
------------------------

We are restarting our experiment on a small set of production nodes as the
code has slightly changed since v1 [2], and there are still a few weeks of
development window to soak the changes. We will report back if we observe
any regressions.

Packetdrill tests
-----------------

The packetdrill tests for TIME-WAIT reuse [3] did not change since v1.
Although we are not touching PAWS code any more, I would still like to add
tests to cover PAWS reject after TW reuse. This, however, requires patching
packetdrill as I mentioned in the last cover letter [2].

Thanks,
-jkbs

[1] https://lpc.events/event/18/contributions/1962/
[2] https://lore.kernel.org/r/20241113-jakub-krn-909-poc-msec-tw-tstamp-v2-0-b0a335247304@cloudflare.com
[3] https://github.com/google/packetdrill/pull/90

Signed-off-by: Jakub Sitnicki <jakub@...udflare.com>
---
Changes in v2:
- Pivot to a dedicated msec timestamp for entering TIME-WAIT state (Eric)
- Link to v1: https://lore.kernel.org/r/20241204-jakub-krn-909-poc-msec-tw-tstamp-v1-0-8b54467a0f34@cloudflare.com

Changes in v1:
- packetdrill: Adjust TS val for reused connection so value keep increasing
- Link to RFCv2: https://lore.kernel.org/r/20241113-jakub-krn-909-poc-msec-tw-tstamp-v2-0-b0a335247304@cloudflare.com

Changes in RFCv2:
- Make TIME-WAIT reuse configurable through a per-netns sysctl.
- Account for timestamp rounding so delay is not shorter than set value.
- Use tcp_mstamp when we know it is fresh due to receiving a segment.
- Link to RFCv1: https://lore.kernel.org/r/20240819-jakub-krn-909-poc-msec-tw-tstamp-v1-1-6567b5006fbe@cloudflare.com

---
Jakub Sitnicki (2):
      tcp: Measure TIME-WAIT reuse delay with millisecond precision
      tcp: Add sysctl to configure TIME-WAIT reuse delay

 Documentation/networking/ip-sysctl.rst                     | 14 ++++++++++++++
 .../networking/net_cachelines/netns_ipv4_sysctl.rst        |  1 +
 include/net/inet_timewait_sock.h                           |  4 ++++
 include/net/netns/ipv4.h                                   |  1 +
 net/ipv4/sysctl_net_ipv4.c                                 | 10 ++++++++++
 net/ipv4/tcp_ipv4.c                                        |  7 +++++--
 net/ipv4/tcp_minisocks.c                                   |  7 ++++++-
 7 files changed, 41 insertions(+), 3 deletions(-)